Analyzable as *ēr-ūca, from ēr (“hedgehog”) + -ūca which is likely by analogy with verrūca (“wart, hillock”), named so for the rugged backs of many caterpillars resembling those of hedgehogs. An alternative theory derives the word from Proto-Indo-European *ǵʰer(s)-uk-eh₂, from Proto-Indo-European *ǵʰers- (“to bristle”) (likely of the same ultimate origin as the above etymology), see also Welsh garw (“rough”), Avestan 𐬰𐬀𐬭𐬱𐬀𐬌𐬌𐬀𐬨𐬥𐬀 (zaršaiiamna, “ruffling one's feathers”), Sanskrit हर्षते (harṣate, “bristles”). Latin erūca and its variant urūca denote the plant and the caterpillar. In such cases, usually the animal name is primary and has been extended to the plant (so the rocket can be interpreted as “caterpillar plant”).